The invention relates to the general field of fabricating parts by casting. The invention relates more particularly, but not exclusively, to a feed system for feeding a mold with molten metal in order to fabricate parts by lost wax casting, in particular in a gravity bottom casting configuration.
In known manner, in a lost wax casting method, a wax model of the part to be fabricated is made initially and then a ceramic shell is formed around it so as to form a mold. A molten metal is then cast into the mold, and it is possible to implement directed solidification of the metal in order to obtain the casting after removing the mold. This method is advantageous for fabricating metal parts of complex shape, and it also makes possible to obtain parts that are of monocrystalline structure, e.g. by using a seed or a grain selector duct.
When the liquid metal fills the mold from below solely under the effect of gravity, this is referred to as gravity “bottom casting”. Under such circumstances, a feed system is generally provided for feeding the mold with molten metal from a bush that is situated higher than the mold, and the mold can be filled progressively upwards from the bottom. With bottom casting, the speed of the liquid metal front entering into the mold for the first time at the beginning of casting (also referred to as the first “metal stream”) can be high. In certain circumstances, this speed may be as much as 1.5 meters per second (m/s). This phenomenon can lead to leaks, to inclusions in the mold of particles torn from the ceramic shell, and, sometimes to degradation or shifting of a core present in the mold.
Feed systems are known that comprise a feed duct for conveying the molten metal into the mold, the duct being provided with a bend where it turns sufficiently to reduce the speed of the first metal stream before it reaches the mold, e.g. by turning through 90°. Although such feed systems serve to reduce the speed of the first stream, they lead to new problems at the bend. Specifically, when the first metal stream reaches the bend at a high speed, it strikes against it, thereby leading to extra pressure that can be referred to as a pressure surge. This phenomenon can lead to ceramic particles being torn away at the bend, and can weaken the feed system, which can then suffer from leaks of molten metal.
There therefore exists a need to have a feed system available for conveying molten metal into a mold, but that does not present the above-mentioned drawbacks.